The present invention relates to medical electrical leads generally, and more particularly to implantable defibrillation electrodes and leads.
Early concepts of implantable defibrillators, such as disclosed in Reissue Pat. No. 27,652 by Mirowski, et al, envision an electrode system employing a ventricular endocardial electrode and a plate electrode mounted to the heart directly, subcutaneously, or to the skin. However, it has long been recognized that a totally transvenous system would be desirable in order to simply the use of implantable defibrillators. One such system is suggested in Mirowski, et al U.S. Pat. No. 3,942,536, which discloses a transvenous lead having electrodes intended for location in the right ventricular apex and in the superior vena cava. This electrode system is disclosed as useful for either ventricular or atrial defibrillation. Such systems were eventually tested in human beings, with some success. However, currently available implantable defibrillators typically employ epicardial patch electrodes, alone, or in conjunction with transvenous electrodes.
While systems employing epicardial patch electrodes are workable, a thoracotomy is required in order to apply the epicardial electrodes. It is generally believed that it would be desirable to produce an implantable defibrillation system which entirely avoids the necessity of a thoracotomy, and there has been substantial work directed towards development of such systems, as disclosed in Kallok U.S. Pat. No. 4,727,877, Tacker, et al U.S. Pat. No. 4,708,145, and as disclosed in U.S. application Ser. No. 07/284,957 filed Dec. 15, 1988 by Mehra, for an "Endocardial Defibrillation Electrode System". Other endocardial defibrillation electrodes are disclosed in Gold et al U.S. Pat. No. 4,481,953, Kinney, et al U.S. Pat. No. 4,161,952, Kiekhafer et al U.S. Pat. No. 4,934,049 and in U.S. Pat. application Ser. No. 07/479,928, filed Feb. 14, 1990 by Holleman, et al, for an "Implantable Electrode and Method for Fabrication". The Kinney, Gold and Kiekhafer patents and the Holleman, et al application all disclose endocardial defibrillation leads employing defibrillation electrodes fabricated from elongated coils of biocompatible metal, mounted exposed to the exterior of the defibrillation lead, for location in the right ventricle and other locations within the heart. The above-cited Smits patent and the Mehra application both disclose a variety of endocardial defibrillation electrodes intended for use in the atrium, ventricle and coronary sinus, all of which employ electrodes taking the form of elongated coils of conductive biocompatible metals.
Concurrent with the development of lead systems adapted to treat ventricular fibrillation, there has also been some work directed to the development of lead systems to treat atrial fibrillation. Synchronized cardioversion using two electrodes located on a lead located in the right atrium is disclosed in Charms U.S. Pat. No. 3,738,370. A later system is disclosed in Mirowski et al U.S. Pat. No. 3,952,750, employing one electrode in the atrium and presumably a second electrode at an unspecified location. Neither of these references discloses a specific embodiment for the electrodes located in the atrium.
An electrode lead system specifically designed for atrial defibrillation is disclosed in the article "Elective Countershock in Atrial Fibrillation With an Intracardiac Electrode--A Preliminary Report, by Jain, et al, published in the Journal of the Association of Physicians of India, Vol. 18, pp 821-824, 1970. This lead was provided with a 10 mm silver electrode for location in the right atrium and was tested in conjunction with either a second electrode located in the right atrium or a second, cutaneous electrode located on the left side of the chest wall. A second electrode system specifically designed for use in atrial cardioversion is disclosed in the article "Safety and feasibility of transvenous cardioversion in atrial tachycardia", by Blanc et al, published in Cardiac Pacing, edited by Gomez, Futura Pub. Co., 1985, pp 1526-1529. This electrode system employed a single lead with electrodes located in the atrium and pulmonary artery.